The present invention relates generally to an input buffer for use in an integrated circuit. The present invention more particularly relates to such an input buffer which buffers input digital signals and filters noise.
Integrated circuits are well known in the art. Some integrated circuits are intended for use in digital processing systems in association with other devices external to the digital processing integrated circuit. In many instances, the devices external to the digital integrated circuits generate spurious or noise signals, which, if not filtered, would provide false inputs to the digital integrated circuit.
As a result, input buffering is preferable in digital integrated circuits. Such input buffering assures that valid logic one or logic zero inputs are properly interpreted and filter spurious signals or noise which are generally either shorter in duration than valid logic levels or of lesser magnitude than valid logic levels.
Input buffers have taken different forms. One known input buffer includes a chain of buffering inverters coupled to one or more AND gates. The inverters buffer the input signals to appropriate signal levels and the AND gates differentiate the valid input transitions from noise. Unfortunately, such input buffers impose gate delays and reduce the operating speed of the integrated circuits in which they are employed. In addition, such input buffers require many active devices which occupy considerable integrated circuit surface area to achieve a filtering function.
There is therefore a need in the art for a new and improved input buffer which provides both input buffering and noise filtering. The present invention provides such an improved input buffer which both buffers digital input signals and which filters noise without requiring a large number of active devices on the integrated circuit on which it is employed.